The invention relates to cigar and cigarette lighters, especially those for motor vehicles. More precisely, the invention relates to cigar lighters with a thermal safety device.
Cigar lighters of this kind are already known, comprising a heating body and a knob 1 intended to be engaged in the heating body. This knob 1 includes a heating resistance element 3 placed in a cup 5 (see FIGS. 1 and 2). This heating resistance element can be supplied with electricity via a supply bimetallic strip in contact with the cup when the knob is pushed into the heating position in the heating body. When this cigar lighter is put into use, the knob is pushed in within the body until the cup is latched onto by the bimetallic strip. When the temperature of the heating resistance element is sufficient, the supply bimetallic strip deforms, cutting off the passage of current in the heating resistance element and allowing the releasing of the knob which comes back into gripping position.
However, if a person or an object continues to exert a force on the knob while it is being heated, or if jamming occurs in the knob, the latter can no longer come back into gripping position. A cyclic phenomenon is then set up: the supply bimetallic strip deforms and cuts off the electrical contact, the cigar lighter cools down progressively and the supply bimetallic strip then comes back to its initial position, re-activating the heating until the supply bimetallic strip again deforms so as to cut off the heating. This cycle occurs until external intervention unblocks the knob. Throughout this time, the electrical harness connected to the cigar lighter conducts the heat given off, by the heating cycle, within the heating body. This may entail damage to the insulation of the electrical cables, damage to the cigar lighter itself, as well as other accidents, such as a fire.
This problem is resolved by virtue of a safety bimetallic strip, installed at the bottom of the heating body (in the hottest part of the heating body) and linked to the positive terminal of the electrical circuit of the cigar lighter. Thus, if the cigar lighter becomes abnormally hot, the safety bimetallic strip deforms and comes to touch a metal piece linked to the negative terminal of the electrical circuit of the cigar lighter, thus causing a short-circuit in the cigar lighter. The fuse of the vehicle to which the cigar lighter is linked immediately blows, thus cutting off the energy to the cigar lighter. The latter no longer heats up and any risk of fire or of damage is avoided. However, in order for the cigar lighter to become abnormally hot, it is necessary for the heating resistance element to operate continuously if the knob is pushed in, even when the supply bimetallic strip is in its deformed configuration corresponding to the opening of the electrical contact between this supply bimetallic strip and the knob.
This function is carried out by a safety device 7 (known to the person skilled in the art by the name of xe2x80x9csafety bufferxe2x80x9d), which maintains electrical contact with the knob 1, whatever the configuration of the supply bimetallic strip (FIGS. 1 and 2). The temperature then rises very quickly in the cigar lighter and the safety bimetallic strip deforms so as to cut off the heating, by blowing of the fuse of the vehicle, thus preserving the integrity of the electrical harness.
In the current state of the art, the terminals used for this safety device 7 are such that the electrical contact between this safety device 7 and the cup 5 is formed by the bottom of the cup 5, in proximity to or level with the edge of the aperture of the cup 5 by which the user has access to the heating resistance element (FIGS. 1 and 2).
However, the edge of the aperture of the cup through which the user has access to the heating resistance element corresponds to the hottest area of the cup. This area therefore has a tendency to oxidize. Furthermore, it is in this region that cigar or cigarette ash can be deposited. This causes a degradation of the electrical contact between the safety device and the cup, which is capable of entailing the formation of electric arcs. These poor contacts thus entail an additional heat contribution which is capable of being transmitted to the heating resistance element. This results in degradation thereof, in particular by the formation of electrical contacts between the turns of this heating resistance element. Very rapid degradation of the cigar lighter can then ensue.
An object of the invention is to extend the lifetime of cigar lighters equipped with such a safety device.
This object is achieved, according to the invention, by virtue of a cigar lighter, especially for a motor vehicle, comprising a heating body and a knob intended to be engaged in the heating body, this knob including:
a heating resistance element, placed in a cup and able to be supplied with electricity via a supply bimetallic strip in contact with the cup when the knob is pushed in into heating position,
as well as a safety device maintaining electrical contact with the cup, whatever the shape of the supply bimetallic strip, in order to continue to supply the heating resistance element as long as the knob is pushed in into the heating body in heating position,
characterized by the fact that the electrical contact between the safety device and the cup is formed on the flank of the outer face of the cup.
In effect, by virtue of the invention, electrical contact between the safety device and the cup is made in a region of the cup which is further from the heating resistance element. Hence, even if the electrical contact between the safety device and the cup is not optimal, the additional heat contribution due to this poor contact is not directly and immediately transmitted to the heating resistance element. The latter is therefore protected from excessive additional heat originating especially from electric arcs. Its lifetime is therefore extended.
Advantageously, in the cigar lighter according to the invention, contact between the safety device and the cup is made in proximity to or in the region of that part of the cup having the widest diameter. In fact, this region corresponding to the widest diameter of the cup is spaced away from the region where contact is made between the heating resistance element and the cup. In this way, the heating resistance element is spaced even further away from the area of contact between the safety device and the cup.
Advantageously, the safety device is in the form of a strip, configured overall so as to have a U shape in longitudinal section. Electrical contact between the safety device and the cup is then made in the region of and in proximity to the longitudinal extremities of the strip, while the part of the strip corresponding to the bottom of the U is spaced away from the heating resistance element. This makes it possible to limit the transmission of the heat given off by the heating resistance element to the safety device. The fact that the safety device is thus not subjected to excessively high temperatures limits its corrosion.
Advantageously, the safety device is made of solid brass, so as to be less sensitive to corrosion.
Further advantageously, the safety device is in contact with a safety bimetallic strip, arranged in order to establish a short-circuit in the electrical circuit of the cigar lighter when it deforms under the effect of the excess heat produced in the course of a malfunction of the cigar lighter.
Other aspects, objects and advantages of the invention will be better understood with the aid of the detailed description which follows.